1. Field of the Invention
The present invention relates to image pickup apparatus and method in which a focus action is followed to a zoom action.
2. Description of the Related Art
A digital camera or other image pickup apparatus or an interchangeable lens unit therefor is sometimes mounted with a varifocal type lens or lens unit (hereinafter, referred to as the varifocal lens unit). The varifocal lens unit is advantageous in that it is capable of being small-sized and capable of changing a focal distance (photographing range) to photograph an object that is at a close distance or at a far distance. In the varifocal lens unit, however, a focal position (focusing position) changes with a change of focal distance, and therefore a focus adjustment must be made.
Accordingly, in an image pickup apparatus with varifocal lens unit, a focus action is sometimes performed to drive and move the focus lens interlockingly with a zoom operation so that the focal position does not change during the zoom operation. For example, drive amounts of focus lens corresponding to amounts of zoom operation are stored beforehand in a memory. During the zoom operation, an amount of zoom operation is detected, a drive amount of focus lens corresponding to the zoom operation amount is determined referring to stored contents of the memory, and the focus lens is driven and moved.
In an image pickup apparatus having a main unit attached with an interchangeable lens unit with varifocal lens unit, the focus lens is driven to an in-focus position according to a result of focus detection by a focus detector mounted to the main unit of the apparatus. Some image pickup apparatus of this type is configured to perform a varifocal correction (focus adjustment) at a proper timing when the focus lens is driven into focus during a zoom operation according to a result of focus detection (see, Japanese Laid-open Patent Publication No. H4-350612).
In the image pickup apparatus with varifocal lens unit, however, a focus follow-up delay sometimes occurs. In other words, a focus action (a follow-up movement of the focus lens) sometimes lags behind a zoom action, which is performed responding to the zoom operation. In particular, in a single-lens reflex digital camera of a lens replacement type (such as one disclosed in Japanese Laid-open Patent Publication No. H4-350612) where a manual zoom operation mechanism is used, when a manual zoom operation is performed at high speed, the focus action inevitably lags behind the zoom action responding to the zoom operation. As a result, a large deviation of focal position is caused, which results in a blur state. Therefore, the focus detection cannot be satisfactorily performed. In that case, a focus search operation must be made, resulting in an increase of time required to achieve focusing.
In recent years, the varifocal lens unit has been often used in image pickup apparatuses adapted to moving image photographing. With the image pickup apparatus of this type, an extremely large deviation of focal position is caused at the time of zoom operation, especially, when an object located at a close distance is zoomed to high magnification. Thus, an extremely long time is required to achieve focusing.